Initially, in ozone generation technique, in 1930 Chapman said that among cosmic rays from space and solar light energy, those having a wavelength of not more than 242 nm become oxygen atoms by giving energy to an oxygen molecule, and the oxygen atoms and the oxygen molecules are bonded to generate ozone, and further it has been said that the generated ozone absorbs light having a wavelength of not more than 320 nm, decomposition reaction into oxygen molecules and oxygen atoms proceeds simultaneously, and ozone is generated by a balance between decomposition reaction of oxygen and decomposition reaction of ozone.
In ozone existing in the ozone layer in part of the stratosphere on the earth and having a concentration of approximately 2 to 8 ppm, ozone generation due only to cosmic rays and solar light energy cannot be sufficiently explained from the cosmic rays and the solar light energy, and it has been said that such ozone generation is closely related to the plasma density of the ionosphere in the stratosphere (105 pieces/cm3). In other words, not only oxygen gas absorbs cosmic rays and solar light energy having a wavelength of not more than 242 nm and dissociates into oxygen atoms, but a high-speed electron density of the plasma of the ionosphere collides with oxygen molecules over the earth, so that dissociation into oxygen atoms occurs. In other words, it is said that in the ozone layer, dissociation of oxygen atoms is caused by two effects, that is, by light absorption of cosmic rays and sunlight and electron collision in the plasma of the ionosphere.
It is theoretically proven that an ozone concentration of approximately 2 to 8 ppm is generated by three-body collision between oxygen atoms and oxygen molecules dissociated by those two methods. When the ozone concentration of approximately 2 to 8 ppm of the ozone layer is represented by the number of ozone, it is 4×1012 pieces/cm3, and this corresponds to 107 times the plasma density of the ionosphere (105 pieces/cm3); however, this value is said to be reasonable, considering the fact that a gas density over the earth is 1/100 of the earth's surface (in the atmosphere) and the decomposition rate of ozone is also very low due to collision with a wall.
From around the 1940's, researches on discharge ozone generators have been actively conducted, and ozone concentrations exceeding the ozone concentration of the ozone layer have come to be obtained. In particular, in a silent discharge (dielectric barrier discharge) method via a dielectric, particular attention has been paid to plasma capable of injecting high electric power in a high electric field, and ozone generators of high concentration and large capacity have been developed.
In the 1990's, the oxidizing power of ozone obtained from an ozone generator has been utilized, and a film formation technique of a semiconductor insulating film has gained attention, so that a high-purity ozone gas has been required. In order to obtain the high-purity ozone gas, an ozone generator using a high-purity oxygen gas as a raw material gas has been required. However, in conventional ozone generators, it was clarified that if the high purity oxygen gas is used as the raw material gas, only an ozone concentration of not more than several tens g/m3 (several thousands ppm) could be obtained and research to fundamentally reconsider an ozone generation mechanism in the conventional ozone generator was started. There have been started various positive elucidations on various phenomena such as “relationship between discharge plasma density (electron density) and generated ozone concentration”, “relationship between raw material gas and generated ozone concentration”, “relationship between discharge surface material and generated ozone concentration”, and “regarding ozone decomposition degree in discharge plasma”.
What is noteworthy here is that although it has been conventionally believed that ozone of high concentration exceeding 200 (g/m3) (93,333 ppm) is generated by discharge plasma density (that is, electron density), discharge electron density (1010 pieces/cm3) in an ozone generator is a much higher electron density than the electron density of the ionosphere (105 pieces/cm3). Since the gas density is also very high and there are walls on both discharge surfaces of a discharge space of the ozone generator, not only ozone can be generated by collision of electrons, but in ozone generated by electrons, an amount to be decomposed increases due to collision of generated ozone with electrons and molecules and collision with the wall of the discharge surface, and an amount of ozone generated by electrons of discharge plasma is assumed to be approximately less than several tens (g/m3) (4000 ppm). A sufficient explanation cannot be provided by only oxygen atom dissociation due to collision of ozone generated by a conventional ozone generator with oxygen molecules and high-speed electrons, and a mechanism in which high concentration ozone can be generated has remained unclear.
As a conventional high-concentration ozone generation technique in 2003, there is a prior art document disclosed in Patent Document 1 as an invention relating to catalyst production of oxygen atoms by a raw material gas and discharge, and there are prior art documents such as Patent Documents 2 to 6 as inventions relating to photocatalyst production of oxygen atoms by a material of a discharge surface and discharge.
In the prior art, although high concentration ozone is generated by an ozone generator, there has been discussed a theory that if a raw material gas is a high purity oxygen gas, decomposition of generated ozone is promoted by oxygen gas, and a high concentration ozone gas cannot be taken out. As means for suppressing this ozone decomposition theory, attention has been paid to a nonconductive film on a discharge surface, and further, as an invention relating to suppression of decomposition of ozone generated by a material of a discharge surface in an ozone generator, there are prior art documents such as Patent Documents 7 to 9.
In the technique disclosed in Patent Document 1, as an ozone generator capable of generating high concentration ozone having a concentration of not less than 200 (g/m3) (93,333 ppm), an ozone generator in which nitrogen gas of 0.1% (1000 ppm) to several % (several tens of thousands of ppm) is added to oxygen gas as a raw material gas to be supplied is used. Patent Document 1 describes that the raw material gas described above is used, nitrogen gas added in a slight amount is converted to nitrogen oxide gas by discharge, and this slight amount of nitrogen oxide gas has the ability to catalyze dissociation of a large amount of oxygen molecules and generate a high concentration of oxygen atoms, so that high concentration ozone can be generated and taken out by a three-body collision reaction of the high concentration of oxygen atoms generated through nitrogen oxide and oxygen molecules.
Patent Documents 2 to 6 show that high concentration ozone is generated by applying a photocatalytic substance to a discharge surface.
The techniques disclosed in Patent Documents 7 and 8 are each an invention in which ozone generated in an ozone generator is taken out without being decomposed, and are inventions completely different from Patent Documents 1 to 6.
Patent Document 7 shows that “a transition metal containing alkaline metals, alkaline earth metals, or rare earth elements at position A of the transition metal oxide having a crystal structure in which an atom does not exist at position A of the perovskite structure is made to exist” on a discharge surface of the ozone generator, so that in the ozone generator, high concentration ozone can be taken out without decomposing generated ozone.
However, the specification of Patent Document 7, under the circumstances, has no description indicating how ozone concentration characteristics should be when it is assumed that ozone generated and developed based on a theoretically unknown theory is decomposed, and has description that only that taken-out ozone concentration is high in a compound applied onto the discharge surface. In addition, the description has a poor chemical basis for a perovskite structure and ozone decomposition inhibition effect. Although a demonstration test of ozone generation was carried out with CaTiO3 as a representative metal compound having a perovskite structure, high concentration ozone was not demonstrated at all, and the reproducibility of the effect of Patent Document 7 was impossible.
In paragraphs [0041] to [0045] of the specification of Patent Document 7, it is described that “when 0.5 vol % of nitrogen gas was added to the high purity oxygen gas, there was almost no effect of adding the nitrogen gas”; however, Patent Document 7 does not show the test data as shown in Patent Document 1 but merely describes results based on poor evidence. Even for this test, if the reproducibility test is carried out, the effect of adding nitrogen gas is sufficient, the accuracy of Patent Document 1 is demonstrated, and it is a generally accepted fact in the ozone generator field.
Patent Document 8 discloses an ozone generator “in which a functional substance to hinder a decrease of the ozone concentration is fixed on the surface of a dielectric by a baking fixing agent (that is, the functional substance is contained in ceramic)”; however, the method of the present invention is the fact described in Patent Documents 1, 2 to 4 and 6, and Patent Documents 2 and the like and Patent Document 8 differ only in a functional substance having ozone generation ability and a functional substance to hinder a decrease of the ozone concentration, and differences in production techniques are not recognized. Although it is concluded that the described functional substance is the functional substance (catalytic substance) to hinder the decrease of the ozone concentration, the specification merely describes demonstration data in which high concentration ozone was obtained, and it is unknown whether the factor that high concentration ozone is obtained is due to the factor that hinder the decrease of the ozone concentration.
In general, in catalytic reactions, it is defined by accelerating the reaction of decomposing ozone and oxygen. However, as described in Patent Document 8, evidence functioning to hinder the decrease of the ozone concentration is not sufficiently described in the content of the specification of Patent Document 8.
In Patent Document 9, a functional film limited to an ozone generator surface is shown.